This invention relates to ball and socket pivot joints and more particularly to preloaded ball and socket pivot joints providing variable preload.
With reference to prior art FIG. 1 a conventional metal ball and socket pivot joint is shown at 10' designed for mechanical devices such as automotive suspension systems. The ball joint 10' includes a one-piece ball stud unit 12' received in a housing 13' formed with a socket 21' having an upper opening 14' and a lower opening 15' concentrically aligned on socket principal axis A'. The ball stud unit includes a ball-shaped head 16' having a stem 18' extending therefrom through the housing lower opening 15' The head 16' has its lower semi-spherical portion seated on a lower bearing seat 20'. The housing socket 21' has an upper cylindrical-shaped portion 22' terminating in the upper opening 14' closed by annular cap 24' An upper pressure plate, shown schematically at 26', is formed with an upper bearing seat (not shown) seating a top portion of the head 16'. A rubber pressure ring 36', compressed between the upper cap 24' and the pressure plate 26' exerts a predetermined preload on the ball stud 12'. The pressure ring 36' is preloaded to both take up wear of the bearing surfaces and to prevent unseating of the ball stud 12' during extreme angular movements of the ball stud.
A "side effect" of increasing the ball joint preload is a corresponding increase in angular torque as the amount of angulation increases between the elements interconnected by the joint. It is desirable in automotive suspension systems to reduce the angular torque in a middle range of ball stud angular movement which corresponds to moderate driving speeds and/or passenger loads. At high driving speeds and/or passenger loads, however, the amount of angulation increases between the suspension elements interconnected by the ball joint. As the ball stud approaches its maximum angular movement, increased ball joint preloading is necessary to avoid unseating of the ball stud. Accordingly, a variable preloading arrangement for a suspension ball joint is desirable for both maintaining minimal preload in the middle range of ball stud angular movement while increasing preload during extreme ball stud angular movement.